Observations in the vicinity of wind turbines show, that bats may be killed or injured by wind turbines in operation.
According to investigations there are two ways to injure or cause the death of a bat by a wind turbine.
The first one is that there is a direct collision of the bat with a blade of the wind turbine, when the rotor of the wind turbine is in operation.
The second one is that moving wind turbine blades cause high pressure differences in the surrounding area of the turning blades. Those air pressure differences might cause internal injuries to the bat, e.g. the lungs of the bat may be hurt if the bat passes by.
Thus the direct impact of the turning blade and/or the caused pressure differences of the turning blade may be fatal for the bat.
There are specific bat-species which are endangered in a lot of countries. They are recorded and monitored by help of a so called “red list”. The protection of theses bats is very important even due to their low reproduction rate. In some countries, like the USA, the protection of bats is even a legal requirement.
It is known to stop the rotation of wind turbines in specific time periods to save the bats. It is also known to stop the rotation of the turning blades of the wind turbine if a flying object is approaching towards the wind turbine. For example flying objects are detected by help of radar or by optical detection means.
Document EP 2017470 A1 discloses a wind power generation device capable of reducing collision of a flying object against a blade or bird strike. The wind power generation device includes a tower and a nacelle, which is fixed to the tower. Blades are connected via a hub with the nacelle. An obstacle search device is capable to detect a flying object in front of the wind turbine or on the windward side of the wind turbine. A blade angle controller is used to control a change in the blade-angle. It is even used to stop the rotation of the blades. The obstacle search device searches for the flying object in a continuous manner. If the flying object is detected to approach the wind turbine the blade angle controller changes the blade-angles to stop the rotation.
As a consequence the wind turbine is always stopped when a flying object is detected in the vicinity of the wind turbine. Thus a loss in the energy production is caused.
It is known to scare away flying animals by noise. For example bangs are used for this purpose or even cries of birds of prey. But this solution does not work for nocturnal bats as birds of prey show their main-activity by day. Additionally birds of prey do not hunt bats thus the bats in turn are not scared by birds of prey.
Last but not least the bats are disturbed in their natural behavior by any kind of scare-of-noise. Even a high level of noise might disturb other animals that are not exposed to the effects of the wind turbine.